Fig. 3. An outline of the `groomer' animal (from
Fig. 1) with the lumbosacral
X-radiograph (from Fig. 2)
scaled down and superimposed to illustrate the contrast between the unloaded
excised hyper-extended and the seated flexed, dorsal profiles. The length of
the lumbar column (L1-L6) is approximately 10 cm. Tangents drawn to the
approximate regions of L1 and L6 in the seated animal are shown, and the angle
subtended, approximately -20°, was used to estimate the mean change in
lumbar—lumbar intervertebral joint angle from the unloaded excised to
the loaded in vivo state. The black circle indicates the approximate
position of the centre of mass of the head, forelimbs and upper body in this
particular seated posture. W is an estimate of the `weight' of the
collective head, upper body and forelimb masses, which exerts a flexion moment
about the lumbar spine. The moment arm of W is indicated by the
dashed line and is approximately 10 cm (0.10 m) in this animal.
